1. Field of the Invention
This invention relates to an improved process and apparatus for producing asphalt-concrete.
2. Prior Art Relating to the Disclosure
Bituminous pavements of the plant mix type have generally been produced by drying aggregate in a drum dryer, feeding the dried aggregate into a screening unit capable of separating the dried aggregate into fractions held in a series of storage bins, feeding the fractions in proportioned amounts from the bin units, and mixing the proportioned amounts with a predetermined amount of bituminous composition in a mixing unit of the pug mill type. The drum dryers used to dry the aggregate are generally heated by a forced air burner. Particulate emissions from dryers of this type have posed a problem due to increasingly stringent air pollution regulations. Dust collectors of the "baghouse" type, costing thousands of dollars per plant, are presently the means used to control particulate emissions from drum dryers used in drying aggregate.
Asphalt paving compositions have heretofore been made in a continuous drum type mixing plant, as disclosed in U.S. Pat. Nos. 2,626,875 and 3,423,222, by feeding aggregate into the mixer, contacting it in the mixer with a bituminous composition in the form of an emulsion, and heating the mixture, during mixing of the aggregate and bituminous composition, with a heated gas stream flowing countercurrent to the flow of the aggregate-bituminous composition flow.